This invention relates to substrate processing and, more particularly, to a plasma chemical vapor deposition (plasma CVD) by using a reaction between a gas and radicals obtained from another gas.
As is well known, formation of a film or a layer is one of the primary steps in the fabrication of modern semiconductor devices and, such a film or a layer can be deposited by a CVD process, for example, a thermal CVD process or a plasma CVD process (plasma-enhanced CVD process). Especially, a remote plasma CVD process is an improved one of plasma CVD processes and can form a desired thin film on a substrate or a wafer with suppression of damage arising from plasma.
In an exemplary remote plasma CVD process, two types of gases are used. One type of gas is a plasma material gas that is decomposed, and/or energized, and changed into plasma including radicals and excited species, while another type of gas is a deposition material gas that reacts with the radicals and excited species in a gas phase reaction. For example, the former is oxygen (O2) gas while the latter is monosilane or silane (SiH4) gas. In a remote plasma CVD process, oxygen gas is at first energized and changed into plasma within a plasma generation region. The plasma includes excited species and radicals which are excited oxygen atoms, excited oxygen molecules, oxygen atoms, oxygen molecules, and ozone molecules. The radicals and excited species included in the plasma are supplied into a substrate processing region that is separated or isolated from the plasma generation region. Independently of the excited species and radicals, monosilane gas is also supplied into the substrate processing region, where a gas phase reaction between the oxygen gas and the monosilane gas occurs. The gas phase reaction produces precursors which are for silicon dioxide (SiO2) and are for example SiHx, SiHxOy, SiOy and so on. The precursors are adhered to a substrate or a wafer arranged within the substrate processing region and are subjected to oxidation, thermal dissociation and so forth, so that the silicon dioxide film are formed on the substrate or the wafer. Silicon nitride (Si3N4) film and an amorphous silicon (a-Si) film can be formed in the way similar to the above-mentioned remote plasma CVD process.
Some types of apparatuses and methods for processing with remote plasma CVD techniques are shown in Japanese Patent Laid-Open Nos. H8-167596 and H8-194942, which are incorporated herein by reference.
One problem that arises during such remote plasma CVD processes is that a deposition material gas, such as silane gas, flows back into the plasma generation region from the substrate processing region. In case of silane gas of the deposition material gas, the backward flow of the deposition material gas results in excess formation of hydrogen atoms (H) and/or hydrogen molecules (H2), so that the silicon dioxide film formed on the substrate or wafer includes a great deal of H or OH. The problem is discussed in Japanese Patent Laid-Open No. H8-45858, which is incorporated herein by reference.